A061999 a(n) = 2*a(n-1)^2 - 2*a(n-2)^2 with a(0) = 0, a(1) = 1.

0, 1, 2, 6, 64, 8120, 131860608, 34774439752390528, 2418523320185277177863741363978240, 11698510100560033501377640350194228137500049288930688305497138757632

Offset

0,3

Links

Harry J. Smith, Table of n, a(n) for n = 0..12

Formula

a(n) = A062000(n)/2.

Mathematica

Join[{a=0, b=1}, Table[c=2*b^2-2*a^2; a=b; b=c, {n, 10}]] (* Vladimir Joseph Stephan Orlovsky, Jan 22 2011 *)
nxt[{a_, b_}]:={b, 2b^2-2a^2}; NestList[nxt, {0, 1}, 10][[All, 1]] (* Harvey P. Dale, Apr 05 2022 *)

Prog

(PARI) { for (n=0, 12, if (n>1, a=2*a1^2-2*a2^2; a2=a1; a1=a, if (n==0, a=a2=0, a=a1=1)); write("b061999.txt", n, " ", a) ) } \\ Harry J. Smith, Jul 29 2009
(SageMath)
def a(n): # a = A061999
    if (n<2): return n
    else: return 2*(a(n-1)^2 - a(n-2)^2)
[a(n) for n in (0..14)] # G. C. Greubel, May 01 2022

Crossrefs

Cf. A062000.

Sequence in context: A052522 A372736 A193609 * A066756 A070872 A055685

Adjacent sequences: A061996 A061997 A061998 * A062000 A062001 A062002

Keyword

nonn

Author

Henry Bottomley, May 29 2001

Status

approved